This invention relates to a water distribution system pressure control method and apparatus.
One of the applicant""s prior patents, European Patent No. 574241, the teaching of which is incorporated herein by reference, describes a low power control apparatus for controlling the pressure at the outlet of a valve in a water distribution system by applying a variable pressure signal to one chamber of a dual diaphragm pilot valve. The pilot valve in turn controls the main valve. The variable pressure signal is varied by the operation of a pair of low power solenoid valves, one of which is connected to a source of high pressure and the other of which is vented to atmospheric pressure.
The design concentrates in minimizing power consumption from its battery supply by keeping the pulsed operation of the solenoid valves to a minimum, and trapping a volume of water at a controlled pressure in the second chamber of a dual chamber pilot. The design is inherently low power for it has no requirement for operating solenoid valves when the required pressure is reached and demand (flow) conditions remain the same.
The solenoid valves used in this device are required to be small so that the energy required to operate is kept to a minimum. However, the smaller the solenoid valve, the smaller the orifice size, and the finer the filtration required to prevent solids from interfering with the solenoid valve operation. Using too fine filtering causes frequent blocking of filter and hence loss of operation in most water quality conditions encountered in potable water distribution systems. This compromise between orifice size, energy level and filtration requirement limits the reliability of the system.
Another aspect of the apparatus of EP574241 is to xe2x80x9ctrapxe2x80x9d a volume of water at a given pressure (control pressure) within the control chamber of the valve pilot. Due to the incompressibility of the water and the fact that the pilot stem needs to be free to move to control its outlet pressure, the apparatus relies on the elasticity of the pipe work and the flexibility of the diaphragm (which can change shape to keep the trapped volume constant but allows movement of the stem). In certain conditions where the stability of the valve remains affected, compressibility of the control volume may be provided by an additional reservoir.
A control system for a gas distribution system is disclosed in U.S. Pat. No. 5,047,965 (Zlokovitz).
Adjustment of a gas regulator valve having a spring based diaphragm control pilot valve is effected by supplying or augmenting pressure to the spring side of the diaphragm from a supply of pressurized gas via an electrically adjustable regulator valve under the control of a local microprocessor. This apparatus could not be used with a water pressure control system as water is incompressible and therefore could not be used in one of the chambers of the spring based diaphragm controlled pilot valve.
The present invention aims to provide a control apparatus and method which mitigates some of the above problems.
Accordingly, in a first aspect the present invention provides control apparatus for controlling the pressure of a water distribution system, the apparatus including:
variable gas pressure output means for connection to a suitable control means of the water distribution system, and
a relatively high gas pressure source and a relatively low gas pressure source, each being selectively connectable to the variable gas pressure output means in order to vary the pressure of the variable gas pressure output means.
In this way, a low power control apparatus may be provided without using solenoid valves to control the variable pressure output means.
Preferably the apparatus includes at least one, and most preferably two, piezo valves. Such valves are disclosed in the following patents: U.S. Pat. No. 4,567,394 (EP0191011), U.S. Pat. No. 4,625,139 (EP0191011), EPO565510, U.S. Pat. No. 5,318,271 (EP0547022) and U.S. Pat. No. 5,343,894 (EP0538236), the disclosures of which are incorporated herein by reference.
The principle of a piezo valve is that an element of piezo electric material is moveable on application of a voltage. The movement of the element is used to open/close a small valve orifice. The advantage of this type of valve for this application is that because of the capacitor-like operation of the valve it consumes very little powerxe2x80x94a typical power consumption of a piezo valve is a few micro watts whereas a typical power consumption of a solenoid valve is around 1 watt. Typically, the movement of the element is relatively small and so a piezo valve usually has only a small orifice and is therefore suitable for gas as a medium. For this reason, the invention is particularly suitable for use with a pilot valve in which the change in control pressure can be xe2x80x9camplifiedxe2x80x9d to produce a larger change in the pressure of the valve being controlledxe2x80x94see for example, the dual chamber pilot valve described below with reference to FIG. 9.
As an alternative to using one or more piezo valves, the present invention may instead employ any alternative type of valve which operates at a suitably low power. In this context, low power operation preferably means a power consumption of less than one milii watt, more preferably less than 100 micro watts and most preferably less than 10 micro watts.
Preferably one piezo electric effect valve connects the relatively high gas pressure source to the variable gas pressure output means and a second piezo electric effect valve connects the relatively low gas pressure source to the variable gas pressure output means. By suitable operation of the two piezo valves (e.g. using a controller such as a microprocessor) the pressure of the variable gas pressure output means may be altered. As the piezo valves are effectively xe2x80x9czero powerxe2x80x9d, this provides a very low power way to control the pressure of the water distribution system.
Preferably, the relatively low gas pressure source is atmospheric pressure i.e. the second piezo valve is simply connected between a pipe connected to the atmosphere and the variable gas pressure output means (e.g. an outlet pipe).
Preferably the relatively high gas pressure source is a gas reservoir and the gas may be air. In one embodiment, the pressure in the reservoir is controlled by feeding air into the reservoir from an air pump or other air pressure means via a check valve or other control means. The pressure in the reservoir is preferably monitored using a pressure sensor such as a pressure transducer and, upon receipt of a suitable signal from the pressure sensor, the controller operates the air pump to xe2x80x9ctop upxe2x80x9d the pressure in the reservoir. In this way, the pump need only be operated sporadically and assuming negligible leakage in any pipework between the pump and the first (inlet) piezo valve, the pressure in the reservoir remains substantially constant until air usage takes place by operation of the piezo valve. This also helps provide a low power control apparatus.
By comparison with the pressure control apparatus described in EP 574241, a low power operation is achieved by reducing the power needed to control the valves by replacing the solenoid valves with piezo valves and only energizing the pump where a supply has been utilized for control. Effectively the burden of power consumption is transferred from the solenoid valve operation to the pump operation.
Preferably the first (inlet) piezo valve is of the type which is normally closed when unpowered and the second (outlet) piezo valve is of the type which is normally open when unpowered. This arrangement means that, in the absence of power, the pressure of the variable pressure output means is maintained at atmospheric pressure. Since the pressure of the reservoir may be selected by suitable operation of the pump or other pressure generation means, the variable outlet pressure may be suitably controlled. This, together with operation of the piezo valves, permits full control of the pressure of the water supply system and permits, for example, time dependent control of the pressure as taught in EP 574241.
In a further preferred embodiment, two more piezo valves are provided, one in conjunction with the inlet valve and one in conjunction with the outlet valve, thereby providing two inlet valves and two outlet valves. Depending on the required configuration of operation, the two inlet valves may be in parallel or in series and the two outlet valves likewise. In the embodiment described above where the inlet valves are normally closed when unpowered and the outlet valves are normally open when unpowered, the two inlet valves will be arranged in series with each other and the two outlet valves will be arranged in parallel with each other.
In a further preferred embodiment, the apparatus includes means for limiting the maximum pressure in the reservoir. For example, this can be done by use of a suitable controller e.g. by the software of a microprocessor controller being suitably programmed. Alternatively, this could be done by incorporation by a pressure relief valve or a pressure regulator in conjunction with the reservoir. Limiting the maximum reservoir pressure in this way in turn limits the minimum pressure of the water distribution system. This is desirable as, in the event of a fault, it is advantageous that the pressure of the water distribution system does not fall below a minimum value.
Preferably, the apparatus includes power control means which are operable to supply to power to the piezo valve(s). Preferably the power control means are arranged such that in the event of the controller not operating, the power control means do not supply power to the piezo valve. With the arrangement of piezo valves described above, this would ensure that in the event of a xe2x80x9ccrashxe2x80x9d of the controller, the water supply system will revert to a safe operating pressure. For similar reason, the absence of power (e.g. a flat battery) will produce the same effect i.e. the water pressure system will revert to a safe operating pressure.
Conventionally, a piezo valve requires a relatively high voltage to operate (e.g. 24 volts). It is desired that the control apparatus of the present invention can be powered by, for example, a relatively low voltage e.g. 3.6 volts provided by e.g. a single lithium cell. The control apparatus may therefore include a DC-DC converter means in order to convert the voltage provided by the battery to a suitable voltage to operate the valves. The converter means may be driven by a timing signal provided by the controller and the controller is preferably arranged such that the timing signal will not be generated if the controller crashes. Hence, in this event, the valves will not be energized in the event of a crash and the system will revert to a safe pressure as in the case of loss of power.
Preferably the control means of the water distribution system to which the control apparatus is connectable is a main pressure control valve, such as a pressure reducing valve (PRV). As is conventional, this main valve may be under the control of a pipe valve, such as a dual diaphragm (sometimes known as a dual chamber) pilot valve as taught by EP 574241. In essence, the difference between a dual diaphragm pipe valve and a xe2x80x9cnormalxe2x80x9d single diaphragm pilot valve is that the dual diaphragm pilot valve incorporates an additional control pressure chamber. By varying the pressure in this control pressure chamber, the output pressure of the pilot valve (and hence the outlet pressure of the main valve which it is controlling) may be varied.
FIG. 8 shows an example of a system utilizing a xe2x80x9csandwich platexe2x80x9d dual chamber pilot 20 as disclosed in European Patent No. 574241. The flow of water through the control chamber 5 is controlled by a gate mechanism 8 which is linked to a diaphragm 9. A spring 10 applies force to the rear of the diaphragm 9 and the amount of force supplied by the spring may be varied by an adjustment screw 11.
In a steady state situation (where the outlet pressure Po remains constant) the water pressure in the control chamber 5 will be balanced by the force generated the spring and the gate 8 will remain in a constant position. Thus the flow through the auxiliary pipe 4 will remain constant and the pressure (Pv) to the main valve will remain constant.
If the outlet pressure (Po) to be controlled falls (e.g. through increased demand), the spring 10 causes the gate 8 to open further and the flow through the auxiliary pipe increases. Accordingly, the flow through the venturi 6 also increases which results in pressure Pv decreasing, causing the main valve (PRV) to open further. This results in the control pressure Po rising again and the system should then reach a steady state again at the previously set value of Po.
The pilot valve 20 includes a second chamber 21 which is effectively divided into two portions 22 and 23 by a wall 24. A control pressure Pc effectively acts against the force of spring 10 by virtue of diaphragm 26. The spring is mechanically connected by arm 28 to a gate mechanism 8 which controls the flow through chamber 5. The arm 28 passes through wall 24 and the aperture through which it passes is sealed by a seal 29 so that chamber 23 does not contain any water but instead is vented to atmosphere.
If the control pressure Pc is reduced then the gate 8 will open further thereby reducing pressure Pv and increasing the outlet pressure Po. This is usually referred to as a xe2x80x9cfailsafexe2x80x9d system since in the event that the control pressure fails i.e. falls to zero, the outlet pressure Po will be set to its maximum value (determined by e.g. the main valve PRV).
Other prior art forms of dual diaphragm pilot valves are known.
In a further preferred embodiment, the dual diaphragm pilot valve is of the type described with reference to FIG. 9 and in the applicant""s co-pending U.S. patent application Ser. No. 09/980,431 (unpublished application GB 9913058.5), the disclosure of which is incorporated herein by reference.
Preferably the pilot valve includes
biasing means to control a gate for controlling fluid flow through a control chamber.
a second chamber sealed by a second chamber diaphragm into which control pressure is applicable for also controlling the operation of the gate, whereby in use an increase in control pressure acts to reduce fluid flow through the gate;
wherein the side of the diaphragm against which the control pressure is not applied is in fluid communication with the control chamber.
In this way, a xe2x80x9creverse actingxe2x80x9d dual chamber pilot valve is provided in which the need for any seal in association with the second chamber is avoided.
Preferably, the biasing means is a spring means, e.g. a spring such as a helical spring. Preferably the biasing means is biased so as to open the gate and may be rigidly connected to the gate by a suitable mechanical linkage. Preferably the diaphragm is also rigidly connected to the gate and/or spring via the same or a second suitable mechanical linkage.
Preferably, the control chamber is at least partly or wholly bounded by a control chamber diaphragm in addition to the second chamber diaphragm. Preferably biassing means is located on the opposite side of the control chamber diaphragm to the control chamber. As will be explained in detail later in the specification, by approximately selecting the operational areas of the second chamber diaphragm and the control chamber diaphragm (e.g. those parts of the diaphragm which may move), the effect of the control pressure on the fluid flow through the control chamber (and therefore in use, on the outlet pressure) can be selected.
In a preferred embodiment, the ratio of the area of the control chamber diaphragm to the second chamber diaphragm is 2:1 or less. For example, if the control chamber diaphragm is twice the area of the second chamber diaphragm then a particular drop in control pressure will result in an identical increase in outlet pressure. In a different example, if the area of the second chamber diaphragm is three-quarters that of the control chamber diaphragm then an increase in control pressure of a given amount would cause the outlet pressure to decrease by three times that amount. The particular case in which the second chamber diaphragm area is half that of the control chamber diaphragm effectively replicates the function of the xe2x80x9csandwichxe2x80x9d arrangement described earlier with reference to FIG. 8.
In a further aspect, the present invention provides a method for controlling the pressure of a water distribution system including controlling the pressure of a variable gas pressure output means of a control apparatus, the variable gas pressure output means being connected to a suitable control means of the water distribution system. The method includes the step of selectively connecting a relatively high gas pressure source and a relatively low gas pressure source to the variable gas pressure output means in order to vary its output pressure.
Other preferred features of the method are as explained above with reference to the apparatus of the present invention.
In addition to being used with a water distribution system, the present invention may also be used with a gas or other fluid distribution system.